• npiggin@suse.de's avatar
    fs: introduce new truncate sequence · 7bb46a67
    npiggin@suse.de authored
    Introduce a new truncate calling sequence into fs/mm subsystems. Rather than
    setattr > vmtruncate > truncate, have filesystems call their truncate sequence
    from ->setattr if filesystem specific operations are required. vmtruncate is
    deprecated, and truncate_pagecache and inode_newsize_ok helpers introduced
    previously should be used.
    
    simple_setattr is introduced for simple in-ram filesystems to implement
    the new truncate sequence. Eventually all filesystems should be converted
    to implement a setattr, and the default code in notify_change should go
    away.
    
    simple_setsize is also introduced to perform just the ATTR_SIZE portion
    of simple_setattr (ie. changing i_size and trimming pagecache).
    
    To implement the new truncate sequence:
    - filesystem specific manipulations (eg freeing blocks) must be done in
      the setattr method rather than ->truncate.
    - vmtruncate can not be used by core code to trim blocks past i_size in
      the event of write failure after allocation, so this must be performed
      in the fs code.
    - convert usage of helpers block_write_begin, nobh_write_begin,
      cont_write_begin, and *blockdev_direct_IO* to use _newtrunc postfixed
      variants. These avoid calling vmtruncate to trim blocks (see previous).
    - inode_setattr should not be used. generic_setattr is a new function
      to be used to copy simple attributes into the generic inode.
    - make use of the better opportunity to handle errors with the new sequence.
    
    Big problem with the previous calling sequence: the filesystem is not called
    until i_size has already changed.  This means it is not allowed to fail the
    call, and also it does not know what the previous i_size was. Also, generic
    code calling vmtruncate to truncate allocated blocks in case of error had
    no good way to return a meaningful error (or, for example, atomically handle
    block deallocation).
    
    Cc: Christoph Hellwig <hch@lst.de>
    Acked-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    7bb46a67
fs.h 85.6 KB